The invention relates to a process for manufacturing a seal between two machine parts which together enclose a space in which, at least at times, high pressure and/or high temperature prevail. A curable composition is applied as a sealing means directly onto one or both machine parts at least in the areas which do not directly adjoin the space in which, at least at times, high pressure and/or high temperature prevails, and the two machine parts are built in before the curing of the composition.
The invention relates further to an arrangement of two machine parts connected to each other with a seal therebetween, as well as a piston engine with an engine block and a cylinder head and with a seal arranged therebetween.
A solid seal is usually inserted between the engine block and the cylinder head to seal the cylinder head. The solid seal covers the entire seal surface between the engine block and the cylinder head. Openings in the cylinder head seal are provided in the area of the combustion chambers, the cooling water ducts, the cylinder head screws, etc. The edges of the openings for the combustion chambers are strengthened by metal inserts. The other openings can have rings of silicon beads to ensure sealing at these points. The costs of complicated cylinder head seals as used today to achieve quality standards bear no relation to other sealing solutions.
There is known from GB-A-2 189 253 a process of the type quoted at the outset wherein only one curable composition, which is non-fluid at rest, is used as sealing means.
It is known from DE-A-2 203 485 to form a sealing ring in situ between two flanges by introducing between the flanges a solid, moldable, polyacrylate polymer seal means which is heat curable to an elastomer, the flanges then being pressed onto each other in order to achieve a complete contact between the seal means and the seal surfaces of the flanges, and by finally heating the arrangement in order to convert the seal means to the elastomeric form.
There is known from U.S. Pat. No. 5,116,558 and DE-A-196 32 275 a sealing and bonding method for connecting component parts, especially a method for sealing and bonding metal component parts in the vehicle and engine technology. At least one groove with a filling opening is provided in at least one of the joint surfaces. The component parts are joined together in the desired orientation and a sealing or bonding composition is then filled in through the filling opening until the groove is completely filled.
An elastomeric silicone seal is known from DE-A-44 39 186, the silicone being applied to the housing cover in uncrosslinked state and a predetermined period then being allowed to pass up to partial crosslinking of the silicone before it being brought into the desired shape by means of a punching tool. The silicone is subsequently allowed to crosslink completely.
It is known from DE-C1-37 40 033 to provide a flowable sealing means at the solid, cylinder head, seal end side facing toward the timing case cover. The sealing means is pressed during assembly against the seal step sections of a profile seal which is provided between the cylinder head side and the crankcase side cover part of the timing case cover.
Further, it is known to use curable composition appliable in liquid form for sealing gearbox housing covers and oil sump covers. However, only relatively low temperatures and low pressures occur inside such covers.
The object of the invention is to simplify the manufacture of a seal between two machine parts which enclose a space in which relatively high pressures and/or temperatures prevail.
According to the invention, this object is achieved in that the curable composition is applied in liquid form directly onto one or both machine parts, in that directly around the edge of the high pressure and/or high temperature space, a sealing ring is inserted between the two machine parts into a recess of a seal surface of the peripheral wall of the chamber, the recess being dimensioned so that the pressure required for the seal is exerted on the sealing ring in the assembled state of the two machine parts, and in that the curable composition is used for sealing outside the areas which directly adjoin the space.
According to the invention, the solid seal is thus at least partially replaced by a chemical liquid seal.
Subject matter of the invention is further an arrangement of two machine parts connected to each other with a seal there-between, the seal being produced according to the process of the invention, as well as a piston engine with an engine block and a cylinder head and with a seal arranged therebetween, the seal being formed by a curable composition at least in the areas which do not directly adjoin the combustion chambers.
Because the curable composition is built in before the curing, it is a so-called FIP (=formed in place) product. As opposed to that, a so-called CIP (=cured in place) product would not be built in until after curing.
The curable composition is applied directly onto the seal is surface of one or both machine parts. The application of the curable composition can be totally automated, which results in savings not only due to the absence of the solid seal but also is approx. 300 MPa, there is no such maximum value for the seal according to the invention. Within the compressive strength of the material of the machine parts concerned, the surface pressure can be as high as required.
In the case of larger flanges and therewith larger flange surfaces, in particular with multicylinder engines, relative movements of the two seal surfaces can come about due to the different heating or a different thermal expansion coefficient of the component parts. A destruction of the sealing means and a leakage involved with that can be prevented here by a thicker sealant film by which the sealant can follow this movement. In order also to guarantee a metal-on-metal contact in such a case, a bevel or recess is provided at the inner or outer edges of the sealing surface. The thicker sealant film can also be achieved in the area of this bevel or recess when there is otherwise substantially metal-on-metal contact. The beveling or recessing is as a rule merely to be carried out on one flange side, a sufficient covering of the two flange surfaces having to be heeded. A sealant film can build up in the area of the bevel or recess. The thickness of the seal film is to be designed in accordance with the elasticity of the sealant used and the existing relative movement of the flange surfaces to each other so that the sealant is not destroyed during the whole service life of the assembly group. As a rule, a minimum layer thickness of 0.8 mm is sufficient. Depending on the case of application, the bevel or recess can extend over the whole area or also only over part areas of the flange. It may also be necessary for specific applications on the basis of the geometric circumstances of the flange surface to arrange a groove or groove/slant instead of the bevel or recess. The bevel, recess, groove or groove/slant can already be introduced into the casting to save costs.
Due to the described geometric changes in the flange (bevel, recess, groove, groove/slant), an escape of the excess sealant internally or externally is avoided upon correct dimensioning as well as a sufficiently exact metering of the sealant. A sealant escape, e.g., into the combustion chamber can, consequently, be avoided. With an uncontrolled sealant escape, it can come to damage to the assembly group or subsequent assemblies during operation.
The curable composition is preferably an adhesive on an acrylic or silicone basis, e.g. Loctite 5920, Loctite 5699 or 5999, Loctite 5900 or Loctite 5970. However, other chemical compositions are also conceivable. A curable composition or such a sealant is preferably used which is applicable at temperatures of above 180 EC.
The process according to the invention is particularly suitable for manufacturing a seal between the engine block and the cylinder head of a combustion engine, but is also suitable for the manufacture of flange seals in gas turbines and similar machines.